The estimated game length for Horizon: Zero Dawn has now been revealed. This is just how many hours you are expected to complete the main story.
Horizon: Zero Dawn has around 21 main missions for you to complete in the main story. If you are playing the game on Normal, you can expect to complete the main story in roughly around 30 hours or less. The game is shorter if you choose to play on Easy. There is a Hard and Very Hard mode too so those are even more challenging.
The game has several side-quests for you to finish so this will add even more hours to your playtime. You can go back and finish off the side-quests if you did not do them the first time around.
For an action-RPG this is a generous amount of playing time. It’s certainly longer than several other action games released in other gaming genres.
